Food proteins and polysaccharides (PS) are two key structural components used to control texture, structure, and stability of food materials. Typically, foods contain both biopolymers in the form of complex multicomponent mixtures. Conjugation of protein with polysaccharide has been intensively studied in recent years (Dunlap and Côté, 2005, J. Agric. Food Chem. 53: 419-423), with a significant improvement in functional properties (e.g. solubility and heat stability) over a wide pH range.
Protein-polysaccharide conjugates (PPC) (i.e., proteins covalently linked to polysaccharides) are useful as emulsifiers in foods and beverages. The addition of the polysaccharide stabilizes the protein, and such protein-polysaccharide conjugates have superior functional properties (e.g., gelation, emulsification, solubility, heat/pH stability) compared to the unaltered proteins. A naturally produced protein-polysaccharide conjugate can be found in gum arabic, which contains about 2% covalently bound protein. Gum arabic is used extensively as a natural food emulsifier/stabilizer for emulsions and beverages, as an encapsulation agent for flavor delivery, in gum drops and similar candies, and to control ice crystallization in frozen products. However, the price and availability of gum arabic is extremely volatile due to a variety of growth, harvest, and regional issues. About half of the gum arabic produced worldwide is imported by the US (approximately 30,000 tons). Consequently, there is considerable commercial interest in developing a substitute for gum arabic.
Two main techniques are used to produce covalently linked protein-polysaccharide conjugates: (1) chemical modification using reagents such as carbodiimide, and (2) glycation by exploiting the initial step (i.e., Schiff base step which is well before the browning and other undesirable reactions) of the Maillard reaction between a reducing sugar (e.g., glucose, lactose) and an amino group (e.g., lysine). Chemical modifications usually use toxic reagents that are not desirable for use in food ingredients. The usual glycation procedure involves using dry heating (e.g., 60° C.), and storage of the lyophilized mixtures (protein and PS) for a period of up to several weeks at a specific relative humidity (RH).
The initial step in the Maillard reaction, the formation of a covalent linkage between ε-NH2 amino groups on proteins and carbonyl groups on reducing sugars, has been used to create new ingredients with improved food functionalities. The Maillard reaction is comprised of a complex series of reactions, which simultaneously occur by multiple reaction pathways. Generally, the Maillard reaction occurs in three stages (Hodge, 1953, J. Agric. Food Chem. 1: 928-943). The initial stage consists of the condensation between ε-NH2 amino groups and carbonyl groups, Schiff base formation and irreversible Amadori rearrangement, which leads to the Amadori products. The products at this initial stage are colorless, and there is no absorption in the near-ultraviolet spectrum. The intermediate stage involves sugar dehydration, sugar fragmentation and amino acid degradation. These products result in absorption at 277-285 nm due to the furfural region (Vallejo-Cordoba and Gonzalez-Cordova, 2007, Electrophoresis 28: 4063-4071; Hodge, 1953, J. Agric. Food Chem. 1: 928-943). Products are colorless or yellow in the intermediate stage. The final stage is highly colored (yellow or brown), with the formation of brown pigments called melanoidins.
The conjugation of proteins with polysaccharides (PS) is usually carried out using dry-heat treatment, for example the conjugation of β-lactoglobulin (β-Ig) and dextran, under conditions of about 60° C., 35-40% RH (relative humidity), for about 3 weeks (Dickinson and Galazka, 1991, Food Hydrocoll. 5: 281-296). However, there are several disadvantages for this method. It requires powdered protein and PS materials and a constant temperature and relative humidity (e.g. 79% RH), which must be maintained during the reaction. The time required for the reaction is also significant (e.g. 3-5 weeks at 60° C.). The reaction process also cannot be easily controlled and the products are complicated. Intermediate or final stage products of the Maillard reaction are also typically obtained as indicated by the appearance of undesirable light yellow or brown color, which results in increased absorbance at ≥420 nm (Dickinson and Galazka, 1991; Tanaka et al., 1999, Fisheries Sci. 65: 623-628). Although the conjugation of proteins with PS by the dry heating process has resulted in interesting improvements in functional properties, the dry-heat treatment method is not attractive and, as a result of the significant disadvantages described above, there are few commercial PPC ingredients.
Whey proteins, including β-Ig, have been used to stabilize food emulsions because of their surface active properties (Dickinson, 1997, J. Dairy Sci. 80: 2607-2619). The emulsifying properties of PPC prepared with whey proteins by the dry heating process have been studied extensively. While many types of PS have been tested by this dry heating process little is known about the effect of the molecular weight size of the PS on the properties of the PPC.
To use the Maillard conjugation type of approach to commercially produce viable food ingredients, new methods are needed to induce this reaction in a short processing time and in aqueous protein-PS mixtures instead of the expensive lyophilized samples that have been previously studied. It would be advantageous to formulate new ingredients (e.g., PPC) that provide improved functionality (e.g., emulsion stability) and health benefits in various nutritional products (e.g., reduced allergenicity in infant formulae and reduced astringency in low pH protein-fortified beverages). The present invention addresses these and related needs.